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  • 1
    Electronic Resource
    Electronic Resource
    Environmental mercury and arsenic sources in fossil hydrothermal systems, Northland, New Zealand (2000)
    Springer
    Environmental geology 39 (2000), S. 875-887 
    Details
    ISSN: 1432-0495
    Keywords: Key words Marcasite ; Cinnabar ; Phosphates ; Hot springs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Northland, New Zealand has been affected by natural hot water spring systems depositing elevated concentrations of mercury and arsenic over the past 5 million years. Due to the different erosion levels of these hot water systems, four principal types of mercury and arsenic occurrences are found: active hot springs; layered surface deposits (sinters) deposited by hot springs; highly fractured rock zones formed immediately beneath hot springs; and chemically altered and mineralized rock from the deeper roots of hot spring systems. Mercury occurs principally as cinnabar and as a minor impurity (〈1 wt%) in phosphate minerals and iron sulfides, particularly marcasite. Mercury is irregularly distributed through limonitic cements formed during oxidation. Arsenic occurs as a minor impurity (〈1 wt%) in phosphate minerals and iron sulfides, particularly marcasite. Arsenic is also variably dispersed through limonite, but not necessarily with mercury. Decomposition of marcasite constitutes the most significant source of mercury and arsenic pollution from the studied sites. Release of mercury and arsenic into the environment from marcasite, phosphates and limonite is enhanced by acidification of the sites (down to pH of 2), caused by oxidation of iron sulfides. Mercury and arsenic concentrations of up to 100 parts per billion should be expected in waters near the deposits; these concentrations are in excess of recommended drinking water levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002549900068
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  • 2
    Electronic Resource
    Electronic Resource
    Origin and deposition of a graphitic schist-hosted metamorphogenic Au-W deposit, Macraes, East Otago, New Zealand (1989)
    Springer
    Mineralium deposita 24 (1989), S. 124-131 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Macraes gold-tungsten deposit occurs in a low-angle thrust system in biotite grade Otago Schist. Native gold, scheelite, pyrite and arsenopyrite are found in and adjacent to quartz veins and silicified schist of lenticular reef zones, where the thrust system cuts through graphitic pelitic schist. Mineralization is confined to a shear zone, up to 80 m thick, which is closely sub-parallel to the regional schistosity. Chemical alteration is dominated by silicification, with some addition of Cr and depletion of Sr and Ba. Alteration extends only about 5 m from major veins. Oxygen becomes isotopically heavier away from veins due to temperature decrease as hot fluids penetrated into cooler (250°C?) rock. Graphite within the shear zone rocks has reflectance of 6–7% (in oil), similar to graphite in medium-high grade Otago Schist, and is presumed to be metamorphic in origin. This graphite has acted as a reducing agent to cause precipitation of gold where the thrust system, acting as a conduit for metamorphic fluids, intersects the graphitic schist. The metals were derived from the underlying schist pile which may include an over-thrust oceanic assemblage containing metal-enriched horizons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206316
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  • 3
    Electronic Resource
    Electronic Resource
    Southern Alps Cu-Au hydrothermal system, Westland, New Zealand (1990)
    Springer
    Mineralium deposita 25 (1990), S. 118-125 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The Southern Alps of New Zealand is an actively rising mountain belt which displays a thermal anomaly adjacent to the Alpine Fault, the Australian-Pacific plate boundary. Extensive fluid movement occurs in this uplift zone, resulting in metallic vein mineralization. Gold mineralization is confined to greenschist facies rocks, while younger veins in amphibolite facies rocks near the Alpine Fault are enriched in copper. Transport and deposition of metals in this complex hydrothermal system is governed by interaction between rising metamorphic fluids and downward-percolating meteoric fluid. Metamorphic fluids have equilibrated with graphitic schist country rock and are relatively reduced. Infiltration and mixing of meteoric water increases oxygen activity and decreases sulphur activity in the fluid. Oxidised meteoric water heats up and dissolves Cu during downward percolation. This Cu is deposited as the fluid becomes more reduced. Hence, there is a progressive increase in copper content in the middle portions of the hydrothermal system, especially in the more permeable highly fractured rocks near the Alpine Fault.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00208854
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  • 4
    Electronic Resource
    Electronic Resource
    Meteoric incursion and oxygen fronts in the Dalradian metamorphic belt, southwest Scotland: a new hypothesis for regional gold mobility (1996)
    Springer
    Mineralium deposita 31 (1996), S. 365-373 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Post-metamorphic quartz veins which occur over hundreds of square kilometres in the biotite zone of the Dalradian metamorphic belt consist of three principal types: anhedral quartz with pyrite, anhedral quartz with hematite, and prismatic quartz with hematite or rutile. The oxide minerals in anhedral veins have formed by oxidation of pre-existing sulphides, and gold was mobilized during this oxidation. Anhedral quartz veins formed from an aqueous fluid with up to 5 wt% dissolved salts and 16 wt% CO2 at about 300 °C. Texturally later prismatic quartz crystals formed from a compositionally similar fluid which was undergoing phase separation at the H2O-CO2 solvus at 160–200 °C and 500 to 1200 bars fluid pressure. Oxygen isotope ratios for quartz from the veins range from 12.0 to 15.3‰, with hematite-bearing veins generally isotopically heavier than pyrite-bearing veins. Calculated fluid oxygen isotope ratios range from + 8‰ for pyrite-bearing veins to -2‰ for late prismatic crystals. The mineralizing fluid contained a substantial component of meteoric water whose isotopic and chemical composition evolved with progressive water-rock interaction. Evolution of meteoric fluid composition involved migration of oxidation and oxygen isotope fronts in the down-flow direction as head-driven water passed through structurally controlled fractures in the schist pile. A gold solubility trough occurs for the observed fluid in the oxidation frontal zone. Gold remobilization and reprecipitation occurred progressively as the oxidation front migrated through the schist pile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189184
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  • 5
    Electronic Resource
    Electronic Resource
    Meteoric incursion and oxygen fronts in the Dalradian metamorphic belt, southwest Scotland: a new hypothesis for regional gold mobility (1996)
    Springer
    Mineralium deposita 31 (1996), S. 365-373 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract.  Post-metamorphic quartz veins which occur over hundreds of square kilometres in the biotite zone of the Dalradian metamorphic belt consist of three principal types: anhedral quartz with pyrite, anhedral quartz with hematite, and prismatic quartz with hematite or rutile. The oxide minerals in anhedral veins have formed by oxidation of pre-existing sulphides, and gold was mobilized during this oxidation. Anhedral quartz veins formed from an aqueous fluid with up to 5 wt% dissolved salts and 16 wt% CO2 at about 300 °C. Texturally later prismatic quartz crystals formed from a compositionally similar fluid which was undergoing phase separation at the H2O-CO2 solvus at 160–200 °C and 500 to 1200 bars fluid pressure. Oxygen isotope ratios for quartz from the veins range from 12.0 to 15.3‰, with hematite-bearing veins generally isotopically heavier than pyrite-bearing veins. Calculated fluid oxygen isotope ratios range from +8‰ for pyrite-bearing veins to −2‰ for late prismatic crystals. The mineralizing fluid contained a substantial component of meteoric water whose isotopic and chemical composition evolved with progressive water-rock interaction. Evolution of meteoric fluid composition involved migration of oxidation and oxygen isotope fronts in the down-flow direction as head-driven water passed through structurally controlled fractures in the schist pile. A gold solubility trough occurs for the observed fluid in the oxidation frontal zone. Gold remobilization and reprecipitation occurred progressively as the oxidation front migrated through the schist pile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050044
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  • 6
    Electronic Resource
    Electronic Resource
    Near-surface expression of a young mesothermal gold mineralizing system, Sealy Range, Southern Alps, New Zealand (1999)
    Springer
    Mineralium deposita 34 (1999), S. 163-172 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Carbonate-limonite veins formed in steeply dipping fractures in the upper few hundred metres of basement greywacke in the actively rising Southern Alps of New Zealand. The veins are found commonly in extensional fractures near to, but not in, major faults associated with mountain uplift, and/or sinistral faults which bound mountain ranges. Some of the veins contain sulphides and minor gold deposited as part of incrementally formed fracture fillings. Oxygen isotope ratios of calcite range widely between +6 and +24‰, and calcite δ13CPDB=−5.5 to −11.5‰. The veins formed from isotopically exchanged crustal fluid with a probable meteoric water component. The shallow vein network is the near-surface expression of a tectonically induced hydrothermal system which has deposited gold-bearing veins with a mesothermal style over several vertical kilometres. This vein network has formed in a dilatational zone of the oblique collisional orogen where near-vertical fractures tap deep-sourced fluids. Similar processes acting at the southern end of the Southern Alps in the Miocene resulted in locally rich mesothermal quartz-gold veins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050193
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  • 7
    Electronic Resource
    Electronic Resource
    Gold mineralization without quartz veins in a ductile-brittle shear zone, Macraes Mine, Otago Schist, New Zealand (1999)
    Springer
    Mineralium deposita 34 (1999), S. 382-394 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Greenschist facies schist which hosts the Macraes Mine in East Otago, New Zealand has been pervasively altered by post-metamorphic (lower greenschist facies) fluids over a 120 m thick section perpendicular to foliation. Metamorphic titanite has been replaced by rutile, and epidote has been replaced by a variety of metamorphic minerals including siderite, chlorite, muscovite and calcite. The early stages of this alteration occurred during development of a ductile cleavage associated with kilometre scale recumbent folding. The cleavage was widely overprinted by a subparallel set of spaced (mm scale) microshears which are locally enriched in rutile and hydrothermal graphite. Strain was then concentrated into narrow (m scale) zones where more intensely deformed portions of the rock are crossed and highly disrupted by closely spaced (100 μm scale) microshears. The highly strained rocks show a combination of mylonitic and cataclastic microstructures, including crystal-plastic grain size reduction and recrystallization of micas to form a new foliation. Muscovite has grown at the expense of albite in the mylonitic cataclasites. Hydrothermal alteration was accompanied by addition of pyrite, arsenopyrite and gold without development of quartz veins. Gold precipitated with sulphides during reduction of the fluid by hydrothermal graphite. The whole altered rock sequence was later cut sporadically by mesothermal quartz veins which contain gold, scheelite, rutile, pyrite and arsenopyrite. This deposit displays a continuum of post-metamorphic processes and hydrothermal fluid flow which occurred during uplift of the schist belt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001260050211
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  • 8
    Electronic Resource
    Electronic Resource
    Stable isotopic and fluid inclusion evidence for meteoric fluid penetration into an active mountain belt; Alpine Schist, New Zealand (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Calcite and quartz veins have formed, and are forming, in steeply dipping fissures in the actively rising Alpine Schist metamorphic belt of New Zealand. The fluids that deposited these minerals were mostly under hydrostatic pressure almost down to the brittle-ductile transition, which has been raised to 5-6 km depth by rapid uplift. Some fluids were trapped under lithostatic pressures. Fluids in the fissure veins were immiscible H2O + NaCl-CO2 mixtures at 200-350d̀ C. Bulk fluid composition is 15-20 mol% CO2 and 〈4.3 total mol CH4+ N2+ Ar/100mol H2O. Water hydrogen isotopic ratio δDH2O in the fissure veins spans -29 to -68‰, δ18OH2O -0.7 to 8.5‰, and bulk carbon isotopic ratio δ13C ranges from -3.7 to -11.7‰. The oxygen and hydrogen isotopic data suggest that the water has a predominantly meteoric source, and has undergone an oxygen isotope shift as a result of interaction with the host metamorphic rock. Similar fluids were present during cooling and uplift. Dissolved carbon is not wholly derived from residual metamorphic fluids; part may be generated by oxidation of graphite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1994.tb00033.x
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  • 9
    Electronic Resource
    Electronic Resource
    Grain boundary migration of water and carbon dioxide during uplift of garnet-zone Alpine Schist, New Zealand (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 11 (1993), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Deformed quartz veins in garnet-zone schist adjacent to the active Alpine Fault, New Zealand, have fluid inclusions trapped along quartz grain boundaries. Textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins. Many of the inclusions are empty, but some contain carbon dioxide with densities that range from 0.16 to 0.80 g cm−3. No water, nitrogen or methane was detected. The inclusions are considerably more CO2-rich than either the primary metamorphic fluid (〈5% CO2) or fluids trapped in fracture-related situations in the same, or related, rocks (〈50% CO2). Enrichment of CO2 is inferred to have resulted from selective migration (wicking) of saline water from the inclusions along water-wet grain boundaries after cooling-induced immiscibility of a water-CO2 mixture. Inclusion volumes changed after loss of water. Non-wetting CO2 remained trapped in the inclusions until further percolation progressively removed CO2 in solution. This mechanism of fluid migration dominated in ductile quartz-rich rocks near, but below, the brittle-ductile transition. At deeper levels, hydraulic fracturing is also an important mechanism for fluid migration, whereas at shallower levels advection through open fractures dominates the fluid flow regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1993.tb00154.x
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  • 10
    Electronic Resource
    Electronic Resource
    Shallow-level metamorphic fluids in a high uplift rat metamorphic belt; Alpine Schist, New Zealand (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 6 (1988), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Fluids, some of which are CO2-rich (up to 40 mol.% CO2) and some of which are highly saline (up to 18 wt% NaCl equivalent), are trapped as fluid inclusions in quartz-calcite (∼ metallic minerals) veins which cross-cut the pumpellyite-actinolite to amphibolite facies rocks of the Alpine Schist. Fluids were commonly trapped as immiscible liquid-vapour mixes in quartz and calcite showing open-space growth textures. Fluid entrapment occurred at fluid pressures near 500 bars (possibly as low as 150 bars) at temperatures ranging from 260 to 330° C. Saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low-density CO2-rich fluid. Calcite deposited by these fluids has δ13C ranging from – 8.4 to – 11.5 and δ18O from + 4 to + 13. Isotopic data, fluid compositions and mode of occurrence suggest that the fluids are derived from high-grade metamorphic rocks. Fluid interaction with wall-rock has caused biotite crystallization and/or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks.Fluid penetration through the rock is almost pervasive in many areas where permeability, probably related to Alpine Fault activity, has focussed fluids on a regional scale into fractured rocks. The fluid flow process is made possible by high uplift-rates (in excess of 10 mm/year) bringing hot rocks near to the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1988.tb00405.x
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